This invention relates to an improved dental support structure for crown restoration used in conjunction with a dental implant when the tooth root is no longer present in the patient's gum.
Our prior U.S. Pat. No. 4,480,997 disclosed a new dental post that was adapted for thread cutting insertion into a tooth root. The invention of that patent divided the stem of the dental post into a plurality of legs moveable relative to each other. When inserted, the dental post was rigidly affixed to the tooth by screwing and/or using an adhesive. Such an implant was suitable where the tooth root was intact in the gum.
Where the tooth root is not present it has been customary to employ an implant which is fixed in relation to the jaw bone or has only the limited amount of motion which the implant experiences. It has also been known to provide some resiliency to the implant to prevent fractures of the implant or lysis of the retaining portion of the jawbone. For example, U.S. Pat. No. 4,793,808 employed a support structure that was itself elastomeric. U.S. Pat. No. 3,863,344 also disclosed an implantable dental support surrounded by an elastic material for cushioning on its sides. It included a stainless steel pin within an elastomeric envelope and resting on an elastomeric base, all within a textile sleeve. This reduced the pressure on the bone of the jaw to reduce lysis, but was not specifically designed to provide the degree of motion simulating the motion of a natural tooth.
U.S. Pat. No. 4,731,085 disclosed an enossal implant made of fragile thin walled alumina ceramics for insertion in a jawbone. The implant was designed with a complex internal structure to cushion the torques that could fracture the thin walls and brittle structures of the implant. It provided, in each of several embodiments, a series of elastomeric sleeves surrounding a central cylinder so that sidewise, i.e., lateral torques were cushioned. A complex structure involving close fitting sleeves and machined surfaces allowed some translational motion limited in such a way as to reduce strain. The elastic structures were not designed to provide the feel of a natural tooth, but rather to shift the fulcrum of motion to predetermined locations as compression increased, in order to control torques.
The present invention provides the advantage of toothlike degrees of freedom without the complexity of the prior art by providing an essentially unrestrained off axis movement of the dental support structure within the implant and locating the elastic medium at an extremity of the support structure.